This is a competitive renewal application for the Training Program in Environmental Health Sciences that is based at the Harvard School of Public Health. This is an interdisciplinary and interdepartmental program that currently supports 12 predoctoral and 3 postdoctoral trainees. Twenty-three Harvard University faculty members are listed as preceptors; most of these are in the Biology in Public Health (BPH) program at the Harvard School of Public Health (HSPH) and are members of the HSPH NIEHS Center for Environmental Health (an interdisciplinary unit that fosters research and administers the NIEHS Center Grant ES000002); the remaining preceptors are in the Biological and Biomedical Sciences (BBS) program in the Harvard Medical area. The faculty preceptors are located in the following departments: Cancer Cell Biology, Environmental Health, Nutrition, Epidemiology, immunology and Infectious Disease, Chemistry and Molecular Pharmacology, Microbiology and Molecular Genetics, and Pathology. The home base of this training program is the School of Public Health where there is a strong emphasis on the application of knowledge gained through basic research to the protection of human health from the effects of toxic environmental agents. Its strength derives from this fact as well as the fact that the training faculty has a broad range of skills ranging from structure/function analyses of environmentally relevant macromolecules (e.g., DNA repair and recombination proteins), to molecular epidemiological studies of human gene-environment interactions, to assessments of real-life exposures of human populations to environmental pollutants. The investigators continue to offer an array of basic studies on how bacteria, yeast, cultured mammalian cells, knockout and transgenic mice, and humans respond to environmental agents with emphasis on how the agents are perceived, how signals are transduced to various parts of the cell or animal, and on the biological consequences of toxin exposure. They believe that this program offers an exciting range of research for both predoctoral and postdoctoral training. The proposed training program is also proud of the superb quality of the applicants, the participating departments and the laboratories of individual preceptors. A rigorous training is proposed for both predoctoral and postdoctoral trainees, and it is expected that this training will position the trainees for productive careers in the Environmental Health Sciences in academia, government, etc.